1. Field of Invention
The present invention relates to a semiconductor process, and more particularly to a method for forming HfOx film based on atomic layer deposition (ALD) process.
2. Description of Related Art
MOS is a basic structure widely applied to various semiconductor devices, such as memory devices, image sensors and display devices. An electric device is required to be made lighter, thinner and smaller, in which that MOS transistor needs to be scaled down accordingly. In order to assure the function of MOS transistor is in well performance, a rather thin layer of high-K material, such as HfOx film, is used to serve as a gate insulating layer in the transistor.
The traditional manner to form the HfOx film is based on ALD process, in which each ALD cycle just forms a layer with the thickness of atomic order, such as 0.5 or 0.6 Angstroms. After a number of ALD cycles, an intended thickness of the HfOx film can be formed.
FIG. 1 is a drawing, schematically illustrating a traditional apparatus form forming the HFOx film. In FIG. 1, the traditional apparatus may include a holder 52, which can hold a substrate 54, such as silicon substrate. The substrate 54 is located inside a chamber 50. The chamber has an inlet and outlet, so the material of H2O and HfCl4 can be applied through the chamber 50 by a form of pulses. Due to the reaction between H2O and HfCl4, the HfOx film can be formed. Here, the index x of HfOx ideally is 2. However, the index x for this stage of formation is usually not exactly equal to 2, as usually known in the art.
FIG. 2 is a drawing, schematically illustrating a traditional ALD cycles to form the HFOx. For one ALD cycle, a H2O pulse with pulse time oft may be applied in to the chamber 50 and then a HfCl4 pulse with pulse time oft may be applied after the H2O pulse. The material of HfCl4 may react with the H2O staying on the substrate, so an atomic layer of HfOx can be formed. After a certain number of ALD cycles, the HfOx film with intended thickness can be formed.